Current-driven dynamics of chiral ferromagnetic domain walls

TL;DR

This paper demonstrates that in ultrathin ferromagnets with broken inversion symmetry, chiral domain walls stabilized by Dzyaloshinskii-Moriya interaction can be efficiently driven by current, with their chirality confirmed through experimental dynamics analysis.

Contribution

It provides direct evidence of chiral Néel domain walls stabilized by DMI and explains their current-driven motion in ultrathin ferromagnetic heterostructures.

Findings

Chiral domain walls are stabilized by DMI in ultrathin ferromagnets.

Spin Hall effect drives domain walls in opposite directions depending on material.

Experimental confirmation of domain wall chirality and rigidity.

Abstract

In most ferromagnets the magnetization rotates from one domain to the next with no preferred handedness. However, broken inversion symmetry can lift the chiral degeneracy, leading to topologically-rich spin textures such as spin-spirals and skyrmions via the Dzyaloshinskii-Moriya interaction (DMI). Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin texture enables extremely efficient current-driven motion. We show that spin torque from the spin Hall effect drives DWs in opposite directions in Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a N\'eel configuration with left-handed chirality. We directly confirm the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral. This work resolves the origin of controversial experimental results and highlights a new path towards interfacial design of spintronic devices.